1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display (LCD) device and a method of manufacturing the same, which can increase a transmittance of a high-resolution pixel.
2. Discussion of the Related Art
With the advance of various portable electronic devices such as mobile terminals and notebook computers, the demand for flat panel display devices applied to the portable electronic devices is increasing.
Liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission display (FED) devices, light emitting diode (LED) display devices, organic light emitting device, etc. are developed as flat panel display devices.
In such FPD devices, the LCD devices are being continuously expanded in application field because the LCD devices are easily manufactured due to the advance of manufacturing technology and realize drivability of a driver, low power consumption, a high-quality image, and a large screen.
FIG. 1 is a plan view schematically illustrating a lower substrate (a thin film transistor (TFT) array substrate) of a related art LCD device, and FIG. 2 is a cross-sectional view taken along line A1-A2 of FIG. 1.
In FIG. 1, a lower substrate structure having a fringe field switch (FFS) mode is illustrated, and a common electrode, an upper substrate (a color filter array substrate), and a liquid crystal layer are not illustrated. In FIG. 1, only some of a plurality of pixels are illustrated.
Referring to FIGS. 1 and 2, the plurality of pixels are formed on the lower substrate of the LCD device. A plurality of pixel areas are defined by a plurality of data lines 20 and a plurality of gate lines 10 which are formed on a glass substrate 1 to intersect.
A TFT is formed in each of a plurality of areas in which the plurality of data lines 20 intersect the plurality of gate lines 10. Also, each of the plurality of pixels includes a pixel electrode 40 and a common electrode (not shown).
The TFT includes a gate 32, an active 34, a source 36, and a drain 38. The gate 32 of the TFT is formed by using a gate line, and the source 36 and the drain 38 are formed simultaneously when forming the data line 20.
A gate insulator (GI) 12 is formed between the gate 32 and the active 34. The gate insulator 12 is formed of silicon nitride (SiNx) or silicon oxide
An interlayer dielectric (ILD) 14 is formed all over the substrate 1 to cover the TFT and the data line 20.
A passivation layer 45 is formed on the ILD 14. Here, the passivation layer 45 is formed of photo acryl (PAC) to have a thickness of 2 μm to 3 μm.
A pixel electrode 40 is formed in a display area on the passivation layer 45. The common electrode (not shown) is formed under/on the pixel electrode 40. The pixel electrode 40 and the common electrode are formed of a transparent conductive material such as indium tin oxide (ITO).
A contact hole 50 is formed by removing a portion of the passivation layer 45, for electrically connecting the drain 38 of the TFT and the pixel electrode 40. The pixel electrode 40 contacts the drain 38 of the TFT through the contact hole 50, and a data voltage input through the data line 20 is supplied to the pixel area via the TFT.
Recently, the LCD device applied to mobile equipment requires a high resolution of 400 PPI to 500 PPI exceeding 300 PPI.
When the active of the TFT is formed of amorphous silicon (a-Si), due to the contact hole 50 for connecting the drain 38 of the TFT and the pixel electrode 40, there is a limitation in realizing a high resolution. As a resolution increases, an area of each pixel decreases, but an area of the contact hole 50 should not be reduced. Therefore, a ratio of an area occupied by the contact hole 50 increases in each pixel, and for this reason, an aperture ratio of each pixel decreases, causing a reduction in a transmittance. Due to the decrease in the aperture ratio of each pixel, a luminance of a backlight and power consumption increase, causing a reduction in a competitiveness of a produce.
LCD devices having a high resolution of 400 PPI or more use low temperature poly silicon (LTPS) instead of a-Si. However, in comparison with a-Si, LTPS is relatively high in price, and lowers a price competitiveness of a product.